Electromagnetic relay devices are configured to bring a movable core closer to a stationary core or separate the movable core from the stationary core to thereby contact or separate movable and stationary contacts.
For example, a plunger electromagnetic solenoid, as an example of these electromagnetic relay devices, is disclosed in Japanese Patent Application Publication No. 2012-94435, which is referred to as a published patent document. The plunger electromagnetic solenoid includes a plunger, an exciting coil, a hollow cylindrical stationary core, a hollow cylindrical movable core, and a coil spring as an example of a return spring. The movable core has a first end, a main body, and a second end in its axial direction. The exciting coil is arranged to surround the stationary core. The coil spring is made of a magnetic material and is comprised of a plurality of loops arranged in its axial direction. The coil spring is interposed between the main part of the movable core and the stationary core such that the first end of the movable core, which projects from a corresponding first end of the main part, is located in the coil spring; a second end of the main part is connected to the second end of the movable core.
The coil spring has opposing first and second ends, the first end of the coil spring is mounted to be fitted in a fitting groove formed in the outer peripheral portion of the first end of the main part of the movable core, resulting in the first end of the coil spring being restrained to the movable core.
The outer periphery of the first end of the movable core is tapered from the outer peripheral portion of the first end of the main part of the movable core toward the stationary core. The stationary core has a groove facing the first end of the movable core. The first end of the movable core has an outer end surface facing the stationary core. The groove of the stationary core has a tapered inner periphery conforming to the tapered outer periphery of the first end of the movable core.
The tapered outer periphery of the first end of the movable core, which is to be abutted onto the tapered inner periphery of the stationary core, is located more inwardly than the fitting groove of the outer peripheral portion of the main part of the movable core. The coil spring urges the movable core to be separated, i.e. returned, from the stationary core to its original position. When energized based on a predetermined voltage, the exciting coil pulls the movable core toward the stationary core against the urging force of the coil spring, so that the end surface of the first end of the movable core is abutted onto the stationary core.
The above configuration of the plunger electromagnetic solenoid prevents the end surface of the first end of the movable core from interfering with the coil spring when the exciting coil is energized based on the predetermined voltage. This enables the voltage applied to the exciting coil to be stable. Because the coil spring is made of a magnetic material, adjacent loops in the axial direction of the coil spring pull each other based on the magnetic force generated by the energized exciting coil. This results in the movable core being more easily pulled to the stationary core to thereby reduce a level of the voltage applied to the exciting coil as compared with a case where the coil spring is made of a non-magnetic material.